There is a large volume of literature related to development of devices suitable for ultraviolet (UV) detection, typically used as detectors in systems for the filtration, or chromatographic or electrophoretic separation of bio molecules.
Traditionally, quartz has been the preferred material for use in devices for UV detection because it is UV transparent. However, quartz suffers from a number of disadvantages: it is more expensive than polymeric materials and the manufacturing process for quartz devices is relatively complicated and expensive. Accordingly, quartz devices are not found to be suitable for disposable systems. There is a significant interest in disposable systems, in particular for use in strictly regulated processes, for example separation or purification of chemicals, bio molecules or other components for use in pharmaceutical applications. Materials used in such systems must fulfil the requirements for United States Pharmacopeia (USP) class VI to guarantee that they do not release harmful substances during use. While this criteria has less relevance for systems to be used for analytical purposes, it is a vital criteria for systems intended for preparative purposes. Such systems for preparative purposes should also provide a sterilised environment in order to meet the strict hygiene requirements for such applications. Accordingly, it should be possible to sterilise the system. Sterilisation is herein construed to mean reduction of microbial population.
Equipment can be sterilised by the use of several methods, for example by the use of 100% ethylene oxide gas. However, this method has a number of disadvantages. First, after sterilisation the equipment has to be transferred to an aeration cell, where it remains until the gas has dispersed and the equipment is safe to handle. Further, the gas may not penetrate to all cavities within the equipment to be sterilised, and seals may be stressed. Additionally, gas permeable packaging materials may have to be used, to allow gas to flow through.
Gamma irradiation is another method used to sterilise equipment. Gamma irradiation sterilisation is herein construed to mean reduction of microbial population by the use of gamma irradiation. Typically, a radiation dose of 25 kGy is used for this purpose and the radiation source is typically 60Co, but 137Cs can also be used. The radiation dose should be at least 15 kGy. For radiation doses less than 15 kGy, for example 10 kGy, the regulatory authorities require a list of all the bacteria present in the system to be sterilised, as well as proof that all the listed bacteria have been killed. Therefore it is preferable to use a radiation dose higher than 15 kGy. Acceptance test criteria for sterility following gamma irradiation are provided in the test USP <85>, and include results for microbial burden (CFU/100 ml) and endotoxin levels (EU/ml) in flow through. The use of gamma irradiation overcomes the disadvantages mentioned above for ethylene oxide sterilisation. Packaging of equipment remains intact during gamma irradiation and seals are not stressed. The gamma radiation penetrates deep into most materials, and eliminates the need for gas permeable packaging materials. Following gamma irradiation, the equipment can be used immediately as it leaves no harmful residue or contaminants.
The sterilisation of equipment by gamma irradiation for use in devices for non-UV detection is well known in the art. Thus, for example, continuous culture chambers or flow cells for use in the on-line microscopic study of biofilm growth are available (e.g. Stovall Life Sciences, Inc. website. As visible light is used in such applications, as opposed to UV detection, many materials can be used which still transmit in the visible range even after gamma irradiation.
The use of polymeric materials in devices for UV detection is described in WO02/29397. WO02/29397 discloses the use of cycloolefin copolymer or an amorphous fluoropolymer (preferably a fluoropolymer known as TEFLON AF®) in a device for UV detection. It also discloses the use of TOPAS® (a copolymer of ethylene and norbornene) which is said to transmit UV at >50% efficiency above 250 nm. However, most cycloolef in copolymers (polymers made from norbornene monomers) are not USP classified. Furthermore, many cycloolef in copolymers will block UV radiation after gamma irradiation treatment. In fact, most polymers tend to block UV radiation after having been subjected to gamma irradiation treatment. TEFLON AF® amorphous fluoropolymer is very expensive as raw material, which makes it economically unsuitable for a disposable device.
U.S. Pat. No. 5,885,470 discloses polymer devices made of polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), polyurethane, polysulfone, polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC) and polycarbonate. Each of these materials suffers from disadvantages. According to WO02/29397, PDMS and polyurethane are not injection mouldable, PVC is typically chemically impure, PMMA and polycarbonate are not particularly UV transparent (below 300 nm) and PTFE is typically not optically clear. Furthermore, polysulfone is very expensive both as a raw material and to process.